This invention relates generally to the formation of a dispersion of reactive liquid droplets in a gas stream.
More particularly, this invention relates to the production of a fog-like dispersion of aqueous droplets containing a chemical reagent for reaction with a constituent of a process gas stream.
It has long been common practice to scrub process gas streams with water or with water solutions of chemical reagents to remove noxious gases therefrom. A wide variety of gas-liquid contacting devices have been developed for this purpose. It is also known to contact gas streams with a very finely divided dispersion of liquid reagent-containing droplets, typically having a median diameter of 10 microns or less, to react with noxious contaminants as is shown by the inventor's prior U.S. Pat. No. 4,125,589. This last process has found industrial acceptance, especially for the removal of offensive odors from gas streams such as those produced in rendering plants.
Use of very finely divided reactive droplets to react with noxious gaseous constituents is substantially more efficient than are the more conventional contacting procedures. Individual droplets, being of much smaller size, display a proportionately larger reactive surface area per unit volume of liquid. The number of individual droplets present in a unit volume of reaction zone is substantially increased, often by several orders of magnitude. Consequently, the distance between adjacent droplet surfaces is greatly lessened thus increasing the chance of collision or contact between a droplet and a reactive or noxious molecule or particle. Because the settling rate of tiny (about 10 microns or less) droplets is so slow, contact time between an individual droplet and gas stream is ordinarily not limited by droplet fall time but is instead determined by gas residence time within the reaction zone. All of these result in a greater contact between reactant and gaseous contaminant whereby much more complete reagent usage is achieved so that scrubbing liquid recycle may be eliminated.
The finely divided reactant dispersion is typically formed by use of ultrasonic nozzles of the general type disclosed, for example, in U.S. Pat. No. 2,532,554. One of the difficulties experienced use of such nozzles lies in their small fluid channels and resonator cavities which tend to plug and to wear especially when the chemical reagent used is corrosive.
Another disadvantage of ultrasonic nozzles is in the use of relatively high volumes of compressed air as the atomizing agent. This requires large compressors, and high energy usage to produce the compressed air. There is also a tendency for air expanding from the nozzle to cause freezing during winter operation.